The present invention relates to a color image forming apparatus utilizing an electrophotgraphic method in which in image forming apparatuses such as copiers, printers, facsimile machines and the like, around an image forming body are arranged a plurality of sets of a charging means, an image exposure means and a developing means and during one rotation of the image forming body, toner images are superimposed to form a color image.
Heretofore, multicolor image forming apparatuses have been known in which the same number of image forming bodies, charging means, developing means, etc. as the number of colors necessary to form an image are provided and a single colored toner image formed on each of the image forming bodies is superimposed on an image receiving material to form a color image; an image forming body is rotated a plurality of times and charging, image exposure and development for each color are repeated to form a color image, and during one rotation of an image forming body, charging, image exposure and development for each color are successively performed to form a color image.
However, it has been found that each of the above-mentioned apparatuses has the following problems. The color image forming apparatus in which the same number of the image forming bodies, charging means, developing means and the like as the number of colors necessary to form an image are provided and one-colored toner images are superimposed on a image receiving material to form a color image results in disadvantages such as the increase in volume of the apparatus due to the requirement of a plurality of image forming bodies and transporting members for image receiving materials. On the other hand, the apparatus in which the image forming body is rotated a plurality of times and charging, image exposure and development are repeated for each color to form a color image enables the volume of the apparatus to be small. However, there is limitation such that the size of a formed image should be less than the surface area of the image forming body.
The apparatus in which during one rotation of the image forming body, charging, image exposure and development for each color is successively performed to form a color image exhibits advantages such that there is no limitation on the image size and further, a high speed image formation is possible. Furthermore, for example, Japanese Patent Publication Open to Public Inspection No. 5-307307 proposes that a transparent substrate is employed as a substrate of the image forming body and the decrease in size of an apparatus is accomplished by arranging an image exposure means in the interior of the image forming body.
However, in the developing means utilizing a single component developer, it is necessary to exchange, at different occasions, the developing means for each color when the developer is used up. Accordingly, it is required that each developing means is readily exchanged and the gap between the image forming body and the developing sleeve of the developing means is accurately set to a predetermined value. Furthermore, a method has been employed in which a gap-holding means is allowed to come into contact with the image forming means and the gap between the image forming means and the developing sleeve provided with the developing means is set. However, problems have been caused in that the image forming means is deformed or damaged by the gap-holding means.
Conventionally, portions for holding the image forming means have been structured by forcibly inserting flange materials into both ends of the image forming means. However, when the flange material is forcibly inserted, the portion subjected to forcible insertion is deformed. Thus, it is hard to hold accurate development gaps of a plurality of developing devices which are disposed so as to have predetermined gaps by the gap-holding means brought into contact with the end of the image forming body. A problem is then caused in which no preferable images are obtained. Particularly, when a resin body is employed as that of the image forming body, the deformation is remarkably caused by the forcible insertion of the flange material and the predetermined gap is not held which is disposed by the gap-holding means brought into contact with the end of the image forming body. Furthermore, a problem is caused in which the gap-holding means is vibrated by the vibration of a bearing as a bearing member and an image forming body driving gear.
Furthermore, the inventors of the present invention have investigated a small-sized process cartridge to which a plurality of the developing means are removably attached. However, when attempting to decrease the size of the process cartridge of which enclosure is liable to become a weak structure on account of the above-mentioned developing means removably attached, a large space is required for detaching the developing means. Thus, a problem has been caused in that a reinforcing member such as a stay, etc. which has been employed to reinforce the enclosure of a conventional process cartridge is not provided.
Furthermore, when the reinforcing member is not provided to the enclosure of the above-mentioned small-sized cartridge, the removably attached developing means occupies a large space and the enclosure of the process cartridge becomes weak and is deformed. As a result, it is difficult to hold, at a position having high precision, both of the developing means and the image forming member with which the gap-holding means is brought into contact. Furthermore, when the enclosure of the process cartridge becomes weak to result in deformation, the image forming body is not securely held by both side plates of the process cartridge. As a result, it becomes difficult to position highly accurately and hold both the image forming body and image exposure means which contains the image forming body.